Method of controlling a device for removing flat items of post from a stack

ABSTRACT

The invention concerns a method of controlling a device for removing flat items of post as a function of the spacing of the item of post to be removed from an item of post already removed, the actual spacing between the item to be removed and the removed item being determined, and the item to be removed being removed as soon as the actual spacing corresponds to a nominal spacing. According to the invention in order to reduce the difference between average gaps between the items of post and minimum gaps, the item of post to be removed is first accelerated to an intermediate speed value which is slower than a predetermined final speed. As soon as the actual spacing equals the nominal spacing, the item of post is accelerated to the final speed.

The invention relates to a method and a device for controlling theremoval in accordance with the preamble of the independent claims.

EP 0 167 091 A1 discloses a device for removing flat items of mail froma stack. This device has a controlled removal element which draws offthe respective frontmost item of mail from a stack and pushes it intothe capture area of a pair of driven feed rollers, a measured sectionbeing arranged between the stack output and the feed rollers, the outputsignals of which section are fed to a control circuit. Here, the removalelement is driven to remove an item of mail in such a way that thedistance between the item of mail to be removed and an item which hasalready been removed is determined and the respective distance-measuringresult is corrected by a prescribed value which is dependent on theacceleration travel of the object to be removed, the removal beinginitiated if the magnitude of the distance-measuring result corrected inthis way corresponds to a set point distance value. Here, the use of theprescribed value makes it possible to take into account differentmechanical properties of the different items of mail and their effectduring the acceleration process.

A different behavior of the items of mail during the removal processalso results from the different position of the items of mail in thestack from which the items of mail are being removed. The consequence ofthis is likewise that the central gaps between the items of mail and theminimum gap which must be maintained in order to supply downstreamequipment, such as letter sorting devices, for example, with items ofmail in an optimum way, are different from one another to an undesiredhigher degree. This difference has adverse effects on the throughputrate.

The object of the present invention is to specify a method and a devicefor removing flat items of mail from a stack, with which the differencebetween the central gap between the items of mail and the minimum gapcan be reduced. This object is achieved according to the invention bymeans of the features of the independent patent claims.

The invention is based on the idea that the item of mail to be removedis initially accelerated to an intermediate speed value which is lowerthan a prescribed final speed, and that as soon as the actual distanceis equal to the set point distance, the item of mail is accelerated tothe final speed. The removal of an item of mail to be removed is carriedout as a function of the position of the item of mail with respect tothe removal element.

Advantageous embodiments of the invention can be found in the dependentclaims and the description.

The invention will be explained in more detail below with reference todrawings, in which

FIG. 1 shows a device according to the invention,

FIG. 2 shows a simplified illustration of a device according to theinvention in which the stack from which the items of mail are to beremoved is illustrated.

FIG. 1 shows a preferred exemplary embodiment of a device according tothe invention. Here, a shaft 20 is provided which is fixedly mounted butfreely rotatable, and has a roller 21 attached to it. The shaft 20 alsoprovides pivotable bearing to a rocker 22 which bears the axle 23 of afurther roller 24. A removal strip 25, whose outer surface has a highcoefficient of friction, is led around the roller 21 and the removalroller 24 as an isolating element.

The rocker 22 is supported by means of a schematically indicated spring26, with the result that the respective position depends on the contactforce of the stack of items of mail of which the frontmost item of mail1′ is shown during its removal. The free end of the rocker 22 acts on amicroswitch which is not shown. If the contact force of the stack is toolow, a normally-closed contact of the microswitch closes, causing ageared motor (not shown) to be switched on. This drives a supportingwall at the end of the stack in the direction of the removal roller 24until the aforesaid normally closed contact switches off again after theposition of the rocker corresponding to the pressing force provided hasbeen reached.

The shaft 20 is driven by a servomotor (not illustrated) in a controlledmanner in the direction of the arrow shown by a broken line in theillustration of the roller 20.

The edges pointing in the conveying direction, i.e. the front edges ofthe items of mail located in the stack, bear, more or less firmlyagainst a stop wall 40, which leaves free, toward the removal strip 25,a gap which permits the items of mail to pass through, that is to saythe stack outlet.

In the conveying path a pair of continuously driven conveying rollers 43and 44 are arranged, by means of which the items of mail are positivelyconveyed on as soon as they pass into their capture area. Theseconveying rollers serve also as deflection rollers of conveying belts 48and 49 which are led around further deflection rollers 50 and 51 in theconveying direction. While the driven conveying rollers 43 are fixedlymounted, the conveying roller 44 is resiliently mounted in a knownfashion, for example on a pivoting lever, but this is not illustrated inthe drawing for the sake of simplicity.

Along the conveying path of the items of mail, a measured section 71/71′is arranged adjacent to the stop wall 40. This measured section isdesigned in such a way that its output signals are a measure of thepartial section of the respective measured section traveled through bythe front edge of the item of mail 1′ to be removed by the referenceedge (rear edge) of the previously removed item of mail 1″.

In the exemplary embodiment shown, the measured section 71/71′ is formedby successive light barriers whose light receivers are designated by thereference symbol 71 and their associated light sources by 71′.Photodiodes or phototransistors are used as light receivers.

In addition, a light barrier 73/73′ with light sources 73 which monitorsthe capture area of the conveying rollers 43 and 44 is provided.

These light barrier signals are evaluated by the microprocessor of thecontrol circuit 60. The respective positions of the items of mail 1′ and1″ are determined from the light/dark signals of the light barriers.

FIG. 2 shows a simplified illustration of a removal device in which anumber of items of mail are arranged in a stack 110, the item of mail 1′which is to be removed protruding into the measured section 100/100′. Anitem of mail 1″ which has already been removed is being conveyed betweenthe conveying belts 120. In order to take into account the differentremoval behavior of items of mail with different properties, inparticular also a different position in the stack 110 of items of mail,the removal of the items of mail takes place in two stages, it beingpossible to take into account the position of the item of mail to beremoved with respect to the removal element. This means that the removalprocess of an item of mail to be removed is regulated on the basis ofinformation relating to its own progress, so that the influence ofproperties of the preceeding, already removed items of mail on theremoval process of the item of mail which is just being removed can beexcluded. For this purpose, the item of mail to be removed isaccelerated to a reduced removal speed, referred to below asintermediate speed, for example half the final speed. The removal isthen started if there is already a detectable gap from the precedingitem of mail which has already been removed. This gap must be of such asize that it can still be increased to the set point distance after thestart. Here, the position of the item of mail to be removed can be takeninto account at the moment of starting the removal process, i.e. thedistance from the transferring belts 120. Likewise, the differencebetween the intermediate speed value and the prescribed final speed canbe taken into account. The current distance between the two items ofmail is monitored after the start of the removal process. As soon as theset point distance between the items of mail has been reached, whichdistance is essentially equal to the minimum distance which can still beprocessed in devices downstream, the machine is accelerated to the finalspeed. Here, all that is then necessary is to accelerate to thedifference between the intermediate speed value and the final speedvalue. This occurs more quickly and with less uncertainty than theacceleration to the final speed value. The monitoring of the currentdistance is carried out with the aid of the light barriers and a sectionclock for the conveying belts 120. Preferably, a condition for the startof the removal process is that at least one light barrier of themeasured section 100/100′ is no longer without a light signal.

If the example of the device in FIG. 2 is considered, it is found, forexample, that the removal process is started later if the front edge ofthe item of mail to be removed is located behind the light barrier 6 ofthe diode line, since otherwise an excessively small distance from thepreceding item of mail is produced. On the other hand, the removalprocess is started earlier if the front edge is located in front of thelight barrier 5, since otherwise the distance from the preceding item ofmail would be unnecessarily large.

For the person skilled in the art it is self-evident that the distancebetween the items of mail can be referred to different removal edges,and that changes in the acceleration behavior due to the drive system ofthe removal device and/or the isolating properties of the items of mailto be isolated can be corrected automatically.

What is claimed is:
 1. A method for controlling a device for removingflat items of mail from a stack as a function of the distance between anitem of mail to be removed and an item of mail which has already beenremoved, comprising: determining the actual distance of the item of mailto be removed from the item of mail which has been removed; removing theitem of mail to be removed as soon as the actual distance is greaterthan a set point distance which has been reduced by a prescribedcorrection value, the correction value being selected as a function ofthe acceleration path of the item of mail to be removed; and initiallyaccelerating the item of mail to be removed to an intermediate speed andas soon as the actual distance is equal to the set point distance,accelerating the item of mail to a final speed.
 2. The method as claimedin claim 1, including selecting the correction value as a function atleast one of a position of the to be removed item of mail relative to aremoval element and a difference between the final speed andintermediate speed.
 3. The method as claimed in claim 1, wherein theintermediate speed is selected to be half the final speed.
 4. The methodas claimed in claim 2, wherein the intermediate speed is selected to behalf of the final speed.
 5. A removal device for feeding flat items ofmail from a stack to a conveying element, comprising: a control circuitfor controlling removal of mail items from the stack as a function of anactual distance between an item of mail to be conveyed and an item ofmail which has already been removed; a measuring section, located withina conveying path of the conveying element arranged down stream of thestack, for measuring said actual distance and having output signalsrepresenting the measured actual distance that feed to the controlcircuit; the control circuit having means which correct the respectivelymeasured actual distance by a correction value which is dependent on theacceleration path of the item of mail to be removed, and which initiatesthe removal of the mail item to be removed if the magnitude of thecorrected distance corresponds to a set point distance value; and aremoval element by which the item of mail to be removed is initiallyaccelerated to an intermediate speed which is lower than a prescribedfinal speed, and in that as soon as the actual distance is equal to theset point distance, the item of mail is accelerated to the final speed.6. The device according to claim 5, wherein the control circuit containsonly one clock generator.